Complexation of chitosan with surfactant like ionic liquids: Molecular interactions and preparation of chitosan nanoparticles

Interactions and behavior of chitosan (Ch) with surface active ionic liquids (ILs)- 1-butyl-3-methylimidazolium octylsulfate, [C(4)mim][C8OSO3] or 3-methyl-1-octylimidazolium chloride, [C(8)mim][Cl]-have been probed at the air solution interface and in the bulk in aqueous media at pH 3.0 using a multi-technique approach, viz, tensiometry, conductometry, turbidimetry, dynamic light scattering (DLS), and atomic force microscopy (AFM). At the interface, a strong complexation is observed in Ch-[C(4)mim][C8OSO3] system. Bulk [C(4)mim][C8OSO3] interacts with Ch to form Ch(4)[C(4)mim][C8OSO3] complexes which precipitate out at higher IL concentrations, whereas comparatively weaker Ch-[C(8)mim][Cl] complexes remain solubilized in the solution. DLS measurements showed that the Ch chains contract before the cmc and expands after the cmc upon interaction with both the ILs. Interaction of ILs with Ch resulted in facile preparation of uniformly distributed Ch nanoparticles with good sphericity and control which have been verified using DLS, SEM, AFM, and fluorescence microscopy. The present study provides an understanding of forces governing the complexation behavior of Ch with surface active ILs and their efficacy to produce Ch nanoparticles. (C) 2013 Elsevier Inc. All rights reserved.